In many analytical applications such as liquid chromatography, the volumes of fluids and/or gasses are small. This is particularly true when liquid or gas chromatography is being used as an analytical method as opposed to a preparative method. Such conventional methods often use capillary columns and are sometimes referred to as capillary chromatography. In capillary chromatography, both gas phase and liquid phase, it is often desirable to minimize the internal volume of any and all components within the flow path of the sample stream, such as selection or injection valves, columns, filters, fittings, tubing, check valves, pressure regulators, detectors, and any sensors that may be used to characterize the conditions within the system. One reason for this control of volumes is that a component having a relatively large internal volume will contain a relatively large volume of fluid or gas. When a sample is introduced into such a component, the sample may be diluted, decreasing the resolution and sensitivity of the analytical method. Similar problems exist in connection with other conventional analytical applications, such as mass spectrometry and capillary flow electrophoresis.
Microfluidic analytical applications also involve small sample sizes. As used herein, sample volumes considered to involve microfluidic techniques can range from as low as only several picoliters or so, up to volumes of several milliliters or so. By comparison, more traditional LC techniques historically often involved samples of about one microliter to about 100 milliliters in volume. Thus, the microfluidic techniques and applications described herein involve volumes one or more orders of magnitude smaller in size than historic LC techniques. Microfluidic techniques can also be expressed as those involving flow rates of about 0.5 ml/minute, or less.
Another problem often encountered in microfluidic applications is the adverse effect(s) that environmental noise or interference may have on the equipment and system, thereby possibly affecting the analyses and test results. Such noise may come from a variety of sources, including environmental electric/electronic or magnetic radiation, mechanical vibrations, thermal changes, and the like. As sample sizes to be analyzed become smaller, and as the components of a liquid chromatography system (or other analytical system) become smaller, more sensitive and more delicate, the potential harmful effects of environmental noise on the system and its components, and their performance, become much greater.
Still another problem often encountered with microfluidic applications results from the fragile nature of conventional components. For example, fused silica tubing is often used for such applications, but is extremely delicate. Such tubing can be easily broken if scratched or struck. The fragile nature of such tubing and other components means that an operator using the same, such as by connecting or disconnecting the same to an analytical system, needs to pay greater time and attention to avoid such breakage.